Clutch release apparatus

ABSTRACT

A hydraulic annular slave cylinder (16) for a motor vehicle clutch having an annular body (21) with inner and outer cylindrical sidewalls (22, 23) having a fluid chamber (55) formed therebetween. The inner sidewalll (22) extends axially beyond the outer sidewall (23) and a piston member (41) is sealingly slideable on the radially outer surfaces of the two walls (22, 23). A clutch release bearing (60) is mounted concentrically of the piston member (41) and fluid chamber (55).

This invention relates to a clutch release apparatus for use with motorvehicle clutch actuation systems.

Motor vehicle transmissions frequently comprise a clutch and a gear boxwhose input shaft is driven through the clutch so that the drive of thegearbox can be broken by operation of a hydraulicably operable slavecylinder. It has become more common for the slave cylinder to be anannular slave cylinder arranged concentrically of the gear box inputshaft.

The concentric slave cylinder is frequently fixed to a face of thegearbox housing within the confines of the gearbox bell housing. Due todimensional limitations it is becoming necessary for the concentricslave cylinder to become more compact.

Accordingly there is provided a hydraulic annular slave cylinder for amotor vehicle clutch comprising an annular body having inner and outercylindrical walls forming a hydraulic chamber therebetween, a pistonmember responsive to hydraulic pressure within the chamber and a releasebearing characterised in that the release bearing is mounted on thepiston member so that the bearing is concentric with a hydraulic fluidchamber.

Preferably the inner wall extends axially beyond the outer wall and thepiston member is sealingly slideable on the radially outer surfaces ofthe two walls.

The piston member may be sealed to the inner wall by a first sealmounted on the piston member and may be sealed to the outer wall by asecond seal mounted on the outer wall.

Preferably the piston member comprises a cylindrical side wall and aradially inwardly projecting flange at one end thereof, the cylindricalside wall being slideably supported on the radially outer surface of theouter cylindrical wall, and radially inner flange sealingly engaging theradially outer surface of the inner wail, and annular relase bearing maybe concentric with the fluid chamber formed by the piston member.

The piston member may further include a secondary piston slideablymounted thereon, the secondary piston forming a second fluid chamber,and the annular release bearing is concentric with the second fluidchamber.

Preferably an annular release bearing is mounted on the outer surface ofthe cylindrical sidewall of the piston member.

The invention will be described by way of example and with reference tofollowing drawings in which:

FIG. 1 is a schematic drawing showing a gearbox and clutch assembly fora transmission.

FIG. 2 is a longitudinal cross section through a first slave cylinderaccording to the invention.

FIG. 3 is a cross section through a second slave cylinder showing theconstruction of the body only.

FIG. 4 is a cross section through yet another embodiment of theinvention and

FIG. 5 is an enlargement of a portion of FIG. 4 showing the valvemechanism.

Now with reference to FIG. 1, a motor vehicle transmission includes afriction clutch 11, and a gear box assembly 12. The gearbox assembly 12has an input shaft 13 driven by the clutch 11, and a bell housing 14which houses the clutch and which in use is bolted against a face of aninternal compustion engine (not shown).

The clutch 11 is operated by an annular hydraulic clutch slave cylinder16 arranged concentrically with the gearbox input shaft 13 and in useengages the radially inner ends of the fingers 19 of a diaphragm spring.The slave cylinder is operated by hydraulic fluid pressure generated bya master cylinder (not shown) which is connected to the slave cylinder16 by conduit 17.

Now with reference to FIG. 2, there is illustrated, in the actuatedcondition, an annular clutch slave cylinder 16 arranged concentricallywith the gearbox input shaft 13. The slave cylinder 16 has an annularbody 21 having an inner cylindrical wall 22 and an outer cylindricalwall 23 spaced radially outwardly thereof. The inner wall 22 extendsaxially beyond the outer wall 23. The body 21 comprises two parts, afirst part 26 including the outer wall 23 is formed from cast aluminiumor moulded plastics material (such as glass filled nylon) and has aradially outwardly extending flange 24 with an annular boss 25 on itsrear face for location in the gear box casing 15, and the second part 27is an annular sheet metal pressing including the inner cylindrical wall22 and has a radially outwardly extending flange 28 at its end adjacentthe gear box. The second part 27 is assembled to the first part with theflanges 24, 28 held in contact with a seal 31 therebetween to form afluid chamber 55. The two parts 26, 27 are secured together by swagingradially outwardly projecting ribs 32 in the second part 27 into aninterrupted annular groove 34 formed on a plurality of circumferentiallyspaced radially inward projections 33 on the rear surface of the firstpart 26.

A spigot 35 having an inlet passageway 36 therein is secured in astepped diameter inlet port 37 in the flange 24 by means of a seal 38and securing ring 39.

An annular piston member 41 is slideable on the radially outer surfaces42, 43 of the inner and outer cylindrical walls 22, 23 respectively. Thepiston member 41 comprises a cylindrical sidewall 44 and a radiallyinwardly projecting flange 45 at the end of the sidewall 44 away fromthe gearbox. The piston sidewall 44 is slideable on the outercylindrical wall 23 and is sealed thereto by a plastics sealing ring 46mounted on the outer wall 23 adjacent the end thereof, and isresiliently biased against the inner surface of the piston sidewall 44by an elastomeric ring 47. The elastomeric ring 47 is held in postion bya cylindrical retainer cap 48 whose open base sits against theprojections 33.

A dust seal 49 prevents dirt or other contaminants from entering betweenthe piston and cylinder.

The flange 45 slides on the outer surface 42 of the inner wall 22 bymeans of a bearing ring 51 mounted on the radially inner edge of theflange 45, and is sealed against the outer surface 42 by an adjacentelastomeric annular seal 52 held in an `L` section plastics retainerring 53.

The piston member 41 is biased away from the gearbox by concentricspring 54, housed in the annular hydraulic chamber 55 formed between thetwo cylindrical wails 22, 23 and acting between the retainer ring 53 andthe base of the retainer cap 48.

An annular bearing 60 is secured concentrically to the piston sidewall44 with its stationary bearing race 65 fixed to the piston sidewall 44by any suitable material such as, adhesive, an interference fit, orresilient spring clip. With the slave cylinder 16 in the "at-rest"condition the release bearing 60 is concentric with (i.e. radiallyoutboard of) the fluid chamber 55 so that the axial length of thecylinder/bearing combination is reduced. The rotary race 66 carries anintermediate annular plate 67 that abuts the inner ends of the springfingers.

In the "at-rest" condition the spring fingers 19 bias the piston member41 towards the flanges 24, 28.

In use, a master cylinder generated hydraulic pressure enters the slavecylinder 16 through the spigot 35 and inlet port 37 and enters thechamber 55 through the gaps between circumferentially spaced projections33. The piston member 41 moves axially away from the end flanges 24, 28and applies a release load to the diaphragm spring fingers 19.

Now with reference to FIG. 3, the slave cylinder 116 has an annular body121, formed from two sheet metal pressings 122, 123 which are weldedtogether through their end flanges 128, 124 respectively. The inletspigot 135 is fixed to a raised attachment point 140 formed on the endflange 124 of the outer cylindrical wall 123. An annular boss 125 isformed on the rear face of the flange 128 of the inner cylindrical wall122 for location to the gearbox housing.

With reference to FIG. 4 and FIG. 5, the slave cylinder 216 has a body221 comprising a cast aluminium or moulded plastics first part 266 whichincludes the outer cylindrical wall 223, and a sheet metal second partwhich includes the inner cylindrical wall 222. The two parts 222, 223are joined together at the respective end flanges 224, 228.

The annular primary piston member 241 is sealingly slideable on theradially outer surface of the inner and outer cylindrical walls 222,223. The piston member 241 comprises a radially outer cylindricalsidewall 244, a radially inwardly extending flange 245 and a radiallyinner cylindrical side wall 250. The piston outer sidewall 244 isslideable on a plastics sealing ring 246 mounted on the outer surface ofthe outer wall 223 and an elastic sealing ring 247 is held in positionby a retainer cup 248 which sits on an annular shoulder 249 on theradially inner surface of the outer wall

The piston inner sidewall 250 slides on a plastics sealing ring 251mounted on the radially inner surface of the piston inner sidewall,together with an elastomeric seal 252 acting between the inner sidewall250 and the inner cylindrical wall 222 of the body 221, and anelastomeric ring 253 which acts to bias the sealing ring 251 against theinner cylindrical wall 222.

The primary piston member 241 is biased away from the gear box by anannular spring 254 and an annular follower 255 located within thehydraulic chamber 260 formed between the two walls 222, 223 of the body221. The annular spring 254 preloads the piston member 241 against thediaphragm spring fingers 18 and acts only for the initial piston travel.The spring 254 can be a coil spring or a belleville spring and reactsagainst the retainer cup 248.

A secondary piston 270 is sealingly slideable on the primary pistonmember 241, and comprises a radially outer sidewall 271 having aplastics ring 272 and elastomeric seal 273, that seals against the outersidewall 244 of the piston member 241, and a radially inwardlyprojecting flange 274 having a plastics seal ring 275 and elastomericseal 246 that seals against the inner sidewall 250, to form a secondaryhydraulic chamber 280. The secondary hydraulic chamber 280 is connectedto the first hydraulic chamber 250 through a valve means 282.

The valve means 282 is mushroom shaped having a head 283 and a stem 287which passes through an orifice 288 in the flange 245 of the pistonmember 241. The head 283 of the valve means is located in the secondarychamber 280 and is biased into a closed condition against a seal 284 byan annular belleville spring 285. The stem 287 of the valve means 282can contact the retainer cup 248 when the piston means 241 is in a fullyretracted condition and cause the valve means to open.

The annular clutch release bearing 60 is secured on the outer surface ofthe secondary piston 270 and its rotary race is connected to anintermediate plate 67 to abut the fingers of a diaphragm spring aspreviously described. The bearing 60 is concentric with (i.e. radiallyoutboard of) the secondary hydraulic chamber 280 so that the axiallength of the cylinder/bearing combination is again reduced.

On initial fitting to a vehicle the piston member 241 is held inposition shown in FIG. 4 by plastics delivery stops 290. Whenpressurised hydraulic fluid is introduced into the slave cylinder 216 itwill fill the two chambers 260 and 280. A further pressure will causethe secondary piston 270 to move the bearing plate 67 into abutment withthe diaphragm spring fingers. The area of the secondary piston 270exposed to fluid pressure is about 60% of the area of the primary pistonmember 241 exposed to fluid pressure. Thereafter as fluid pressurebuilds up the stops 290 either burst or may be removed in other ways andthe primary piston member 241 will then move to operate the clutch byexerting a release load on the diaphragm spring fingers. This allows thevalve means 282 to close isolating the secondary chamber 280. When thefluid pressure is released the spring fingers will push against thesecondary piston 270, but since the valve means 282 is closed, theprimary piston 241 is returned by the load in the diaphragm springfingers acting on the secondary piston 270 until the flange 245 abutsthe spring follower 255 and is held away from the fully retractedcondition in an "at rest condition" by the spring 254 at which point thevalve means 282 is held closed by the spring 285.

As the clutch plate wears, the ends of the diaphragm spring fingers movetowards the gearbox pushing the primary piston member 241 and secondarypiston 270 further back towards the flanges 244, 228 causing the valvemeans 282 to abut the retainer cup 248 and open, consequently allowingfluid to exit the secondary chamber 280 through the valve means 282 andthe length of the secondary chamber 280 to decrease.

When the diaphragm spring fingers exert substantially no load on thesecondary piston 270 the spring 254 exerts a preload on piston means 241to move the piston means 241 away from the retainer cup 247 and thevalve means 282 will close.

This effectively means that in an equalibrium condition in which thereis substantially no hydraulic pressure in the chamber 260, the spring254 maintains the valve 282 in a closed condition.

Eventually the secondary piston 270 will abut the flange 224, as shownin dotted outline, when the clutch is fully worn.

The slave cylinders described with reference to FIGS. 2, 3, and 4 may beutilised with prefilled clutch hydraulics systems of the type describedin European Patent 0 146 283.

I claim:
 1. A hydraulic annular slave cylinder for a motor vehicleclutch comprising an annular body having inner and outer cylindricalwalls forming a hydraulic chamber therebetween, a primary pistondisplaceable in response to hydraulic pressure within the chamber, asecondary piston mounted on the primary piston and displaceabletherewith, and a release bearing operatively connected with thesecondary piston, the secondary piston forming with the primary piston asecond hydraulic chamber of variable length and volume and beingconnected to the first hydraulic chamber through a valve means so thatthe length of the secondary chamber and hence the position of thesecondary piston relative to the primary pistons is adjustable tocompensate for clutch wear.
 2. An annular slave cylinder as claimed inclaim 1 in which the primary piston includes a radially outercylindrical sidewall which is slidably supported on a radially outersurface of the outer cylindrical wall, a radially inwardly projectingflange, and a radially inner cylindrical wall which sealingly engagesthe radially outer surface of the outer wall, and the secondary pistoncomprises an outer cylindrical wall which slidably engages the outercylindrical sidewall of the primary piston and a radially inwardlyprojecting flange which sealingly engages the inner cylindrical sidewallof the primary piston.
 3. An annular slave cylinder as claimed in claim1 in which the valve means is arranged to be open when the primarypiston is in fully retracted condition, and to be closed when theprimary piston is held in an "at-rest" condition away from the retractedcondition allowing the secondary piston to retract relative to theprimary piston when the valve means is open to compensate for clutchwear.
 4. An annular slave cylinder as claimed in claim 3 in which thevalve means is a mushroom valve having a head and a stem, the stemextending through an orifice in the flange of the primary piston and thehead being biased against a seal in the closed condition, the stem beingabutable against a fixed location on the annular body to open the valvemeans.
 5. An annular slave cylinder as claimed in claim 1 in which thearea of the secondary piston exposed to fluid pressure is up to 60% ofthe area of the primary piston exposed to fluid pressure.
 6. A clutchrelease apparatus as claimed in claim 1 in which the release bearing ismounted on the secondary piston concentrically of the second hydraulicchamber.
 7. An annular slave cylinder as claimed in claim 1 in which theouter cylindrical wall and an end flange thereof are formed from amoulding or casting, and the inner cylindrical wall is formed from asheet metal pressing, and the inner wall is secured to the outer wall bydeforming a portion of an end flange of the inner wall around a portionof the end flange of the outer wall.